1. Field of the Invention
This invention relates to a dial input device which forms the input block of an information processing unit of a printing apparatus or the like.
2. Prior Art
Conventionally, a dial input device of this kind includes a dial rotatably mounted as a character entry key on a support frame and having the hirakana letters representative of the Japanese syllabary and the alphabet letters circumferentially evenly assigned thereto, and a push button arranged inside the dial as a settling key for settling an input. The dial is annuluar or ring-shaped, and the push button has a circular shape for being fitted in the ring-shaped dial. The dial incorporates a click mechanism and is rotated together with the push button in both directions to make a click stop whenever it is rotated through an angle corresponding to each of the hirakana or alphabet letters circumferentially evenly assigned thereto. The click mechanism of the dial is comprised of a toothed gear-shaped portion formed on the peripheral bottom surface of the dial and a plate spring for clicking into each recess of the toothed gear-shaped portion.
According to the conventional dial input device, patterns utilized in identifying an input of any of hirakana letters and alphabet letters are obtained e.g. by bringing eight brushes provided on the dial and eight contact members provided on the support frame into sliding contact with each other. The eight contact members are each arranged on the support frame in a manner concentric with the dial. Each contact member in an annular form has electrically conductive and electrically non-conductive portions arranged in a mixed and alternating manner. The eight brushes are arranged on the dial in a manner corresponding to the eight contact members. The identifying patterns composed of eight bits are obtained based on continuity and discontinuity between each of the eight brushes and each of the eight contact members. The hirakana letters and the alphabet letters are identified or represented by the identifying patterns.
A first problem with this kind of conventional dial input device is that since it is required to arrange a plurality of brushes radially so as to obtain a required number of identifying patterns, the dial is inevitably designed to have an increased radial width, and the diameter of the push button is reduced accordingly. The respective diameters of a dial and a push button are generally defined from the ergonomic point of view. An excessively large or small dial or push button is hard to handle, and can be a cause of an erroneous operation of the device by the user.
A second problem with the conventional dial input device is that since the plate spring, employed in the click mechanism, is directly engaged with the toothed gear-shaped portion of the dial, frictional resistance against sliding of the dial is large, so that clicking rotation of the dial can be impaired due to aging of the click mechanism i.e. abrasion of the gear-shaped portion. Further, the plate spring is difficult to adjust for the optimum spring force, which makes it difficult to set a manipulating force required of a user such that he can turn the dial in a smooth agreeable manner.
A third problem with the conventional dial input device is that the push button rotates together with the dial. This does not interfere with operation itself. However, when an indication such as "SETTLE" is printed on the push button, the indication turns with rotation of the dial. This is not sightly.